This invention relates to phase locked loop circuits which generate an output signal with a frequency that repeatedly sweeps across a certain frequency band until an input signal having the same frequency as the output signal is detected; and more particularly, it relates to those circuits of the above type which provide compensation for an electrical parameter in the phase locked loop that drifts.
In the prior art, many circuits have been disclosed which employ a sweep circuit with a phase locked loop to generate a signal that sweeps across a band of frequencies. In particular, a computerized search of U.S. patents that contain the words "phase locked loop" AND "sweep circuit" has identified the following sixty-six patents.
______________________________________ 1. 5,091,702 2. 5,068,731 3. 5,014,340 4. 5,013,978 5. 4,993,048 6. 4,955,083 7. 4,942,393 8. 4,916,405 9. 4,885,632 10. 4,876,737 11. 4,870,382 12. 4,852,123 13. 4,852,086 14. 4,837,853 15. 4,833,416 16. 4,817,192 17. 4,796,102 18. 4,794,623 19. 4,774,439 20. 4,749,960 21. 4,636,736 22. 4,591,910 23. 4,555,707 24. 4,546,388 25. 4,514,706 26. 4,507,617 27. 4,499,434 28. 4,497,211 29. 4,470,145 30. 4,463,288 31. 4,434,669 32. 4,422,096 33. 4,419,760 34. 4,413,274 35. 4,335,383 36. 4,320,356 37. 4,316,154 38. 4,297,650 39. 4,286,286 40. 4,275,363 41. 4,272,705 42. 4,262,264 43. 4,253,117 44. 4,246,546 45. 4,240,100 46. 4,220,914 47. 4,206,420 48. 4,193,030 49. 4,146,843 50. 4,123,725 51. 4,105,932 52. 4,104,680 53. 4,020,490 54. 4,009,448 55. 4,007,400 56. 3,978,411 57. 3,973,250 58. 3,958,186 59. 3,913,028 60. 3,904,817 61. 3,902,121 62. 3,872,455 63. 3,871,020 64. 3,793,594 65. 3,673,430 66. 3,626,426 ______________________________________
However, of these sixty-six patents, only five also include the word "compensation". Those five patents in the above list are numbered 4, 5, 24, 58, and 62. Each of those patents have been analyzed by present inventor; and none of the five patents disclose a phase locked loop with compensation circuitry which enables the output signal to track a sweep voltage while a circuit parameter in the phase locked loop drifts with time/temperature/component selection. Such a circuit is taught only by the present invention.